The use of chains of pre-opened bags to form packages is well known. Such chains of bags are disclosed and claimed in U.S. Pat. No. 3,254,828 entitled FLEXIBLE CONTAINER STRIPS (the Autobag patent). A commercial version of a machine described and claimed in U.S. Pat. No. 3,815,318 entitled PACKAGING APPARATUS, and in other patents deriving from the application that resulted in this patent (the H-100 patents), has been sold commercially by Automated Packaging Systems, Inc. under the designation H-100. A machine described in U.S. Pat. No. 4,899,520 entitled PACKAGING APPARATUS AND METHOD includes an ability to use two chains of interconnected bags while packaging and has been sold commercially by Automated Packaging under the designation H-200.
With each of these machines, a pair of driven nip rolls are adjacent a load station. In the majority of cases, a coil of so-called "bags-on-a-roll" is mounted on a mandrel to supply a web in the form of a chain of pre-opened bags to be fed through the machine. During set-up the web is fed from the supply along a path of travel through a so-called dancer arrangement, then through any accessory devices such as imprinters or hole punchers that may be provided, and thence through a section of the machine known as a bagger to the nip rolls. In order to feed the web through the bagger, it is necessary to open or remove a cover and hand-feed the web over and under rolls delineating the path of travel to the nips. While some machines such as that shown and described in U.S. Pat. No. 4,928,455 issued May 29, 1990 under the title "Packaging Machine and Method," facilitate the feed by having certain of the rolls elevated when the cover is opened, the feed of the web during set-up is nonetheless a manual, time-consuming operation.
When the machine is in use, the nip rolls are relied on to pull the web from the supply through the machine. If tensioning of the web through the machine is not consistent, the machine will not function properly and a number of problems can manifest themselves. These problems include improper registration of a bag at the load station with a resultant poor quality package, improper registration of the web through accessory devices with a result that they do not function properly, partial or complete separation of successive bags in the web section disposed along the path of travel which respectively result in poor packages or machine shut-down.
Inconsistent web tension and its attendant problems can result from a number of causes such as improper dancer adjustment, a poorly wound supply coil, the functioning of accessory devices, and in the case of certain machines such as that shown and described in U.S. Pat. No. Re: 32,963 issued Jun. 27, 1989 under the title "Packaging Apparatus and Method," web feed reversal to effect separation of a loaded bag. In addition, the speed at which these prior machines could operate, do at least in part to limitations of the dancer arm and brake arrangements used, is limited.
Another shortcoming of these prior machines involved changing from a "bags on a roll" supply to a "wig-wag" box (a box that has the web folded back and forth in multiple rows and layers) supply. In order to change from a roll to a box set-up, an accessory to the machine had to be added, which involved a time-consuming procedure as did the reverse set-up of box to roll.
The H-100, H-200 and competitive machines each have two legs that serve as supports for a bagger. When "bags on a roll" are used, each supply roll is supported on a mandrel extending between the two legs. Mounting a supply roll supporting mandrel on such a machine is difficult.
Prior to a bag being loaded on an H-100, a burst of air blows the bag open. After the opening of a bag, the bag sometimes is not held open satisfactorily for the loading process. Additionally, the supply of air that keeps the bag open is continuous with the result that excessive quantities of air can be trapped and bag deflators are often required.
With certain types of products, the nip roll assemblies of these bagging machines tend to inhibit the loading of the bags as well as interfere with bag opening air flow. Separation of the nip rolls is difficult and time-consuming if separation is necessary, such as to clear a web jam.
With a standard H-100 machine, the nip roll assembly is located in one fixed "standard" location. If wide bags are used, the standard location of the assembly causes difficulty in opening bags in that the opening tends to be elliptical rather than circular. As a result, loading of the bags is difficult. One solution to this problem with an H-100 is to have an operator manually load the bags and advance the web through use of a foot pedal that caused a stepper motor to drive one of the nip rolls. This slows the bagging process. Another solution is to lower the bag sealing section. This is a tedious and time consuming procedure.
Another limitation of these machines is they do not function well if the pressure of the air supply is irregular. For example, consistent seal pressure is necessary if high-quality seals are to be formed repetitively and inconsistent seals can result from irregular air pressure.
A further limitation of these machines results if perforations in front and back layers of a web are not in appropriate longitudinal registration. Detectors on these machines cannot properly detect the ends of bags if the perforations are offset longitudinally because when perforations of one layer are aligned with a detector, the other layer interferes with the detection.